The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The invention relates to a skidding system for an offshore installation or vessel, such as an offshore wind turbine installation ship (OWTIS), comprising at least one set, e.g. a pair, of rails (also known as skid beams), and one or more carriages (also known as pallets or carts) for supporting loads and moving the loads along the rails, e.g. from a storage position to an operating position, in particular within the reach of a crane to offload the loads from the vessel, and/or vice versa. The invention further relates to a method of skidding loads on an offshore installation or vessel.
As explained in U.S. Pat. No. 3,486,737, when it is desired to move a heavy load on a support in a straight line or in an arc, the moving sometimes is done by skidding the load. For example, when drilling wells from a platform at sea it is customary to skid the drilling rig on the platform from one well location to another. This is commonly done by means of double acting hydraulic cylinders that skid the rig in a series of short steps, between which the pistons are retracted in the cylinders for the next stroke. In the apparatus according to U.S. Pat. No. 3,486,737, a load (6) is slid along a support (3) by a horizontally extendable device (10), a roller (18) being lifted on actuation of the device in one direction to transfer at least some of the load to the roller and thence through a friction shoe (20) to the support.
U.S. Pat. No. 3,033,525 also addresses skidding and relates to a force-transmitting device for moving one member relatively to another.
In modern skidding systems, the handling of loads, such as subsea modules or heavy weight structures (e.g. Xmas trees, process modules, jacket foundations, PLEMs), on open deck demands a high degree of safety for both equipment and personnel. Existing deck skidding systems typically comprise integrated or on-deck skid rails, push-pull, rack and pinion or winch driven carriages. Lay-out and integration with other systems are preferably optimized for efficient deck logistics. For each project, such as a jacket foundation installation project, new skidding carriages to support the loads on the skidding rails of the vessel have to be developed and built.